pkey_free • man page

pkey_alloc, pkey_free - allocate or free a protection key

pkey_free • man page

pkey_alloc, pkey_free - allocate or free a protection key

pkey_free (2)

Leading comments

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Since the Linux kernel...

(The comments found at the beginning of the groff file "man2/pkey_free.2".)

NAME

SYNOPSIS

DESCRIPTION

pkey_alloc()
allocates a protection key (pkey) and allows it to be passed to
pkey_mprotect(2).

The
pkey_alloc()
flags
argument may contain zero or more disable operations:

PKEY_DISABLE_ACCESS

Disable all data access to memory covered by the returned protection key.

PKEY_DISABLE_WRITE

Disable write access to memory covered by the returned protection key.

pkey_free()
frees a protection key and makes it available for later
allocations.
After a protection key has been freed, it may no longer be used
in any protection-key-related operations.

An application should not call
pkey_free()
on any protection key which has been assigned to an address
range by
pkey_mprotect(2)
and which is still in use.
The behavior in this case is undefined and may result in an error.

RETURN VALUE

On success,
pkey_alloc()
returns a positive protection key value.
pkey_free()
returns zero.
On error, -1 is returned, and
errno
is set appropriately.

ERRORS

EINVAL

pkey,
flags,
or
access_rights
is invalid.

ENOSPC

(pkey_alloc())
All protection keys available for the current process have
been allocated.
The number of keys available is architecture-specific and
implementation-specific and may be reduced by kernel-internal use
of certain keys.
There are currently 15 keys available to user programs on x86.

This error will also be returned if the processor or operating system
does not support protection keys.
Applications should always be prepared to handle this error, since
factors outside of the application's control can reduce the number
of available pkeys.

VERSIONS

pkey_alloc()
and
pkey_free()
were added to Linux in kernel 4.9.
Glibc support is not yet available.

CONFORMING TO

The
pkey_alloc()
and
pkey_free()
system calls are Linux-specific.

NOTES

pkey_alloc()
is always safe to call regardless of whether or not the operating system
supports protection keys.
It can be used in lieu of any other mechanism for detecting pkey support
and will simply fail with the error
ENOSPC
if the operating system has no pkey support.

The kernel guarantees that the contents of the hardware rights
register (PKRU) will be preserved only for allocated protection
keys.
Any time a key is unallocated (either before the first call
returning that key from
pkey_alloc()
or after it is freed via
pkey_free()),
the kernel may make arbitrary changes to the parts of the
rights register affecting access to that key.

EXAMPLE

SEE ALSO

COLOPHON

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